Why is one sales rep's email blocked when others aren't?

Summary

When a single sales representative experiences email blocking issues while their colleagues do not, the causes are multifaceted, spanning technical configurations, content quality, recipient-side factors, and sending practices. Ultimately, the recipient decides what constitutes spam. Factors such as a flagged IP address, poor sender reputation stemming from spam complaints, and suboptimal list hygiene contribute significantly. Different sending infrastructures and inconsistent sending behavior, such as aggressive cold emailing, can trigger filters. Recipient-side filtering, content quality (including spammy phrases and lack of personalization), and technical configurations like missing SPF, DKIM, or DMARC records also play key roles. Adequate email address warm-up procedures are critical as well. SMTP error codes and the possibility of irritated mail administrators further add to the complexity.

Key findings

  • Recipient-Centric Spam Determination: The determination of whether an email is considered spam ultimately rests with the recipient's email client.
  • Sender Reputation and IP Address Flagging: A poor sender reputation and a flagged IP address greatly increase the chances of emails being blocked.
  • Recipient-Side Filtering: Recipient email servers may implement specific rules or filters that disproportionately affect a particular sales representative.
  • Suboptimal Content: Content containing 'spammy' phrases, lacking personalization, or failing to engage recipients can trigger spam filters.
  • Poor List Hygiene: Sending emails to unengaged users or neglecting to verify email addresses can negatively impact deliverability.
  • Inadequate Email Warm-Up: Insufficiently warming up new email addresses before bulk sending can lead to increased blocking rates.
  • Varying Sending Infrastructure: Differences in email clients, ISPs, or SMTP servers among sales representatives can result in inconsistent deliverability.
  • Inconsistent Sending Behavior: Sudden sending volume spikes, aggressive cold emailing, or sending to unsubscribed recipients can trigger filters.
  • Missing Authentication Records: Lack of proper SPF, DKIM, and DMARC records can negatively affect deliverability.

Key considerations

  • Prioritize Recipient Relevance: Always ensure that emails are wanted and relevant to the recipients to minimize spam complaints.
  • Monitor Sender Reputation: Actively monitor sender reputation metrics and address any issues promptly.
  • Implement Robust List Hygiene Practices: Regularly clean and verify email lists to remove unengaged users and invalid addresses.
  • Standardize Sending Infrastructure: Adopt a standardized sending infrastructure across the sales team to ensure consistent deliverability.
  • Regulate Sending Patterns: Avoid sudden sending volume spikes or aggressive cold emailing practices.
  • Optimize Email Content: Create engaging, personalized content that avoids spammy phrases and is relevant to the recipients' interests.
  • Implement Authentication Protocols: Properly configure SPF, DKIM, and DMARC records to authenticate emails and improve deliverability.
  • Conduct Email Warm-Up: Properly warm up new email accounts over time before high-volume sending.
  • Investigate Recipient-Side Issues: Explore any potential filtering rules or blocks implemented by recipient email servers.

What email marketers say
12Marketer opinions

When one sales representative's emails are blocked while others are not, the issue stems from various factors, ranging from sender-specific issues to recipient-side configurations. Sender reputation, IP address flagging, content quality, and email list hygiene play significant roles. Recipient-side filtering, potentially due to irritated administrators or specific security rules, can also lead to blocks. Inadequate email address warm-up, technical errors, or variations in sending behavior can further contribute to deliverability problems. Ultimately, a combination of sender-specific practices and recipient-defined policies determines whether an email is accepted.

Key opinions

  • Sender Reputation: A poor sender reputation, due to previous spam complaints or blacklistings, significantly increases the likelihood of emails being blocked.
  • Recipient-Side Filtering: Recipient email servers may have specific rules or filters blocking emails from a particular sales rep, irrespective of other reps' deliverability.
  • Content Quality: Low-quality content, 'spammy' keywords, or lack of personalization can trigger spam filters and lead to email blocks.
  • List Hygiene: Poor email list hygiene, including sending to unengaged users, is a primary driver of deliverability problems.
  • Warm-up process: Not correctly warming up a new email address will result in a spike in blocked emails.

Key considerations

  • Monitor Sender Reputation: Regularly monitor sender reputation using tools and services designed for this purpose.
  • Review Email Content: Audit email content for 'spammy' keywords and ensure personalization to improve engagement and avoid triggering filters.
  • Clean Email Lists: Implement rigorous list hygiene practices, including removing unengaged users and regularly verifying email addresses.
  • Check Recipient-Side Configurations: Investigate whether recipient email servers have specific rules or filters affecting the blocked sales rep, by contacting the recipient.
  • Warm up correctly: Warm up new emails over a period of time to avoid being flagged for spam.
Marketer view

Email marketer from NeilPatel.com shares that if one sales rep's IP address has been flagged for spam, even if the others haven't, their emails are more likely to be blocked.

December 2022 - NeilPatel.com
Marketer view

Email marketer from Reddit explains that sender reputation is key. If the one rep's email address or domain has a poor reputation due to previous spam complaints or blacklistings, their emails will be more likely to be blocked.

March 2025 - Reddit
Marketer view

Email marketer from Woodpecker shares that the main reasons for low deliverability is either technical errors, content or low engagement rates. That one person could have any number of these issues, which is why only they are getting blocked

February 2022 - Woodpecker
Marketer view

Email marketer from Folderly shares that one person may not have sufficiently warmed up their email address before beginning bulk sending or cold emails. If one person has not done this and the others have, this would lead to an increase of blocks on only 1 address

May 2021 - Folderly
Marketer view

Email marketer from Email Geeks explains that the receiver decides what emails they want or don’t depending on content or other (local to them) settings, and there's no “setting” in Gmail which can make 3rd party receivers accept the email.

November 2022 - Email Geeks
Marketer view

Email marketer from Gmass shares that deliverability relies on the sender's reputation, the recipients engagement and the content. If one persons content is of a low quality, it could indicate why only they are getting blocked

January 2025 - Gmass
Marketer view

Email marketer from Email Marketing Forum suggests that the issue may be on the recipient's end. The recipient's email server may have specific rules or filters that are blocking emails from that particular sales rep, even if the other reps' emails are not affected.

March 2023 - Email Marketing Forum
Marketer view

Email marketer from Mailjet.com shares that poor list hygiene is a major reason for deliverability problems, and ensuring you are sending to engaged users is key.

December 2022 - Mailjet.com
Marketer view

Email marketer from Sendinblue.com explains that even if the email is not spammy, some phrases can trigger spam filters. It suggests avoiding 'spammy' keywords and using personalized content.

December 2023 - Sendinblue.com
Marketer view

Email marketer from Email Geeks shares it might be worth seeing if you should give up on the recipient org too- there's a chance your rep has irritated a mail admin that's decided to block you out of irritation (or worse)

April 2023 - Email Geeks
Marketer view

Email marketer from Email Geeks explains that a 554 “security error” hints at something within the email being blocked. And the other 550 errors hint at the fact hat the receiver (platform) decided they don’t want email from that specific email address anymore.

June 2023 - Email Geeks
Marketer view

Email marketer from Reply.io shares that even if the email is technically correct in terms of IP and reputation, spam filters still need to know if users want to see it. Poor content could be an example of one reason to get blocked.

September 2021 - Reply.io

What the experts say
3Expert opinions

The reason one sales rep's email is blocked while others aren't can be attributed to multiple factors. Ultimately, the recipient determines what is considered spam, regardless of the sender's intent. Technical differences in sending infrastructure (ISPs, email clients, SMTP servers) can lead to disparate treatment by receiving servers. Furthermore, inconsistent sending behavior, such as sudden volume spikes, aggressive cold emailing, or sending to unsubscribed recipients, can trigger filters and result in blocked messages for that specific rep.

Key opinions

  • Recipient Determines 'Spam': The recipient's email client, not the sender, ultimately decides if an email is spam.
  • Inconsistent Infrastructure: Variations in sending infrastructure among sales reps can lead to different treatment by receiving servers.
  • Erratic Sending Behavior: Inconsistent sending patterns, particularly aggressive cold emailing or sending to unsubscribed recipients, can trigger filters.

Key considerations

  • Recipient Perspective: Always consider the recipient's perspective and ensure emails are wanted and relevant.
  • Standardize Infrastructure: Standardize the sending infrastructure across the sales team to ensure consistent deliverability.
  • Monitor Sending Patterns: Monitor and regulate sending behavior to avoid sudden spikes or aggressive practices.
Expert view

Expert from Email Geeks explains that the sender can’t dictate if something is “spammy” or not - only the recipient can make that call. That’s the email client doing its job correctly.

July 2021 - Email Geeks
Expert view

Expert from Spam Resource explains that one potential reason is different sending infrastructures. If the sales reps are using different email clients, ISPs, or SMTP servers, their emails could be treated differently by receiving servers. This is especially true if one rep's setup has a poorer reputation or isn't properly configured.

August 2021 - Spam Resource
Expert view

Expert from Word to the Wise shares that inconsistencies in sending behavior, even within the same organization, can trigger filtering. If one rep's sending volume spikes suddenly, or if they engage in practices like aggressive cold emailing without proper authentication, their messages may be flagged while others are not. They also mention it depends who the email is being sent too, if they are only emailing people who unsubscribed previously, this also causes issues.

March 2023 - Word to the Wise

What the documentation says
4Technical articles

When a sales representative's emails are blocked while others aren't, various technical configurations and policies come into play. Google highlights the importance of adhering to Gmail's bulk sender guidelines, particularly setting up SPF, DKIM, and DMARC authentication. Microsoft's Exchange Online Protection (EOP) uses content filters, connection filtering, and Spam Confidence Levels (SCL) to block spam. RFC Editor details SMTP 550 errors, indicating refusal by the recipient server for reasons like sender blocks, spam flagging, or full mailboxes. Mimecast specifies that emails can be blocked because of content or if the email address has been previously blocked due to security policies.

Key findings

  • Gmail Bulk Sender Guidelines: Failure to adhere to Gmail's bulk sender guidelines, especially regarding SPF, DKIM, and DMARC, can lead to blocks.
  • Exchange Online Protection (EOP): Microsoft's EOP uses content filters, connection filtering, and SCL to identify and block spam.
  • SMTP 550 Errors: SMTP 550 errors indicate the recipient server has refused the message due to various reasons.
  • Content/Blocked Email Address: Mimecast blocks emails because of its contents or if the email has been previously blocked.

Key considerations

  • Implement Authentication: Ensure SPF, DKIM, and DMARC authentication are correctly configured for the sending domain.
  • Monitor Content: Review email content to avoid triggering spam filters or violating content policies.
  • Check Block Lists: Verify that the sending email address or domain is not on any blocklists.
  • Address SMTP Errors: Investigate and address the root cause of any SMTP 550 errors.
Technical article

Documentation from Mimecast details that an email may be blocked due to content within the email being blocked because of security policies setup. Also, the email address may have been blocked previously.

March 2024 - Mimecast
Technical article

Documentation from Microsoft explains that Exchange Online Protection (EOP) uses a variety of techniques to identify and block spam. It may be blocking emails from the one sales rep due to content filters, connection filtering, or spam confidence levels (SCL).

April 2022 - Microsoft Learn
Technical article

Documentation from RFC Editor provides details on SMTP error codes, specifically 550 errors, which indicate that the recipient's email server has refused to accept the message. This could be due to a variety of reasons, including the sender being blocked, the content being flagged as spam, or the recipient's mailbox being full.

December 2024 - RFC Editor
Technical article

Documentation from Google explains that Gmail has specific guidelines for bulk senders, and failing to comply can lead to emails being blocked or sent to spam. It recommends checking that the sales rep is following these guidelines, including setting up SPF, DKIM, and DMARC authentication.

July 2021 - Google Support